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Adapting Video for VI Learners

Optimising brightness

When we surveyed the accessibility of video to VI students, about three quarters said that they were sensitive to glare, and about a quarter said that this made viewing videos impossible for them. However, we wouldn't like to take this at face value: it could be that ambient lighting was not right; or that a poor compromise was being made between multiple light sources; or possibly that students weren't in a position to adjust the screen brightness to meet their own needs.

Ambient lighting

The classroom or lecture theatre should have some background lighting to avoid fatigue. Take care to position light sources and monitors to avoid screen glare, especially where lights are low, or not diffuse.

Some people, because of loss of vision in the central field, may prefer to have low or no background lighting to increase pupil size and thus widen the field of vision, and you may be able to reach a compromise with the needs of the rest of the group which can help.

If you suffer from glare, remember that TV's and computer screens are light sources in themselves. If you already have absorptive lenses it may help to wear these while viewing.

Multiple light sources

Classrooms have multiple light sources: TV's and monitors, overhead projectors and slide projectors, and the lighting on real objects such as maps, and physics demonstrations. Getting the balance right will be difficult. Students and their teacher will be aiming to even out 'hot spots'; get the overall brightness for each information source at the right level; and avoid making things difficult for fully sighted students.

The last will be easier to achieve if other students are kept aware of why the environment is as it is: their vision has a lot of leeway to accommodate variations if goodwill is there.

Hot and dark spots are trickier. If you have to alternate between a TV monitor or computer VDU and an overhead projection screen (OHP) you will find that the OHP screen is likely to be much brighter. Teachers: see if your OHP has a variable brightness switch. Students: if OHP over-brightness is still a problem for you, whether viewing with a telescope/binoculars or without low vision aid, it would be worthwhile asking if the lecturer could use a yellow acetate to filter out some of the glare coming from the white background.

Remember as you modify the lighting on demonstrations, maps and the like, that above and below an optimal level of brightness you will start to compromise other desirable visual qualities. For instance, at high and low brightness levels, colour subtlety is lost. Contrast is also compromised: washed out at high brightness levels, and greyed out at low.

You can help with the contrast problem when you are lighting three-dimensional solids by off-setting one light source to generate shaded areas (what photographers refer to as 'modelling'). Don't overdo it though, or you will lose detail in the shadows.

Screen brightness

Satisfying the needs of both sighted and visually impaired pupils or students with just one screen is likely to prove difficult (and not just because of brightness adjustments). The ideal situation is to have a second monitor for the VI student, and provide him or her with their own controls for it. As we have said elsewhere, as with the video recorder the best approach is for students to control their set through a remote infra-red hand controllers.

For those reading these notes on video-enabled multimedia we've simulated this below: use the controller to experiment with different brightness levels.

All TV's and monitors have a brightness control but its effectiveness will vary depending on the quality of the set. Adjusting brightness alone doesn't usually help very much - all parts of the image increase in luminance together, producing a washed out effect which does little to reveal detail (and might even make the situation worse when overdone, as contrast diminishes). The likelihood is that as brightness is adjusted, you will also want to adjust contrast to compensate.

To get better control, consider using an external Audio Visual control box. AV controls, normally used for video editing, offer a wide range from black level to high luminance.